OSLO  Humans are responsible for the worst spate of extinctions since the dinosaurs and must make unprecedented extra efforts to reach a goal of slowing losses by 2010, a U.N. report said on Monday.

Habitats ranging from coral reefs to tropical rainforests face mounting threats, the Secretariat of the U.N. Convention on Biological Diversity said in the report, issued at the start of a March 20-31 U.N. meeting in Curitiba, Brazil.

"In effect, we are currently responsible for the sixth major extinction event in the history of earth, and the greatest since the dinosaurs disappeared, 65 million years ago," said the 92-page Global Biodiversity Outlook 2 report.

Apart from the disappearance of the dinosaurs, the other "Big Five" extinctions were about 205, 250, 375 and 440 million years ago. Scientists suspect that asteroid strikes, volcanic eruptions or sudden climate shifts may explain the five.

A rising human population of 6.5 billion was undermining the environment for animals and plants via pollution, expanding cities, deforestation, introduction of "alien species" and global warming, it said.

It estimated the current pace of extinctions was 1,000 times faster than historical rates, jeopardising a global goal set at a 2002 U.N. summit in Johannesburg "to achieve, by 2010, a significant reduction in the current rate of biodiversity loss".

"Unprecedented additional efforts' will be needed to achieve the 2010 biodiversity target at national, regional and global levels," it said. The report was bleaker than a first U.N. review of the diversity of life issued in 2001.

NOT ABATING

According to a "Red List" compiled by the World Conservation Union, 844 animals and plants are known to have gone extinct in the last 500 years, ranging from the dodo to the Golden Toad in Costa Rica. It says the figures are probably a big underestimate.

"The direct causes of biodiversity loss -- habitat change, over-exploitation, the introduction of invasive alien species, nutrient loading and climate change -- show no sign of abating," the report said.

Despite the threats, it said the 2010 goal was "by no means an impossible one".

It urged better efforts to safeguard habitats ranging from deserts to jungles and better management of resources from fresh water to timber. About 12 percent of the earth's land surface is in protected areas, against just 0.6 percent of the oceans.

It also recommended more work to curb pollution and to rein in industrial emissions of gases released by burning fossil fuels and widely blamed for global warming.

The report said, for instance, that the annual net loss of forests was 7.3 million hectares (18 million acres) -- an area the size of Panama or Ireland -- from 2000-2005. Still, the figure was slightly less than 8.9 million hectares a year from 1990-2000.

And it said that annual environmental losses from introduced pests in the United States, Australia, Britain, South Africa, India and Brazil had been estimated at more than $100 billion.

About 300 "invasive species" -- molluscs, crustaceans and fish -- have been introduced to the Mediterranean from the Red Sea since the late 19th century when the Suez Canal opened.

It gave mixed overall marks for progress on four key goals.

It said there was "reasonable progress" towards global cooperation but "limited" advances in ensuring enough cash and research. It estimated that annual aid to help slow biodiversity losses sank to $750 million from $1 billion since 1998.

And it said there was "far from sufficient" progress in better planning and implementation of biodiversity decisions and a "mixed" record in better understanding of biodiversity.